Patent GB-881832-A (GB)
Title: Improvements in or relating to the bonding of metals to bodies comprising semiconductive or brittle materials
IPC: H01R12/55
Filed: 1957-10-29
Abstract: 881,832. Semi-conductor devices; ceramic or glass to metal seals; mounting terminals. WESTERN ELECTRIC CO. Inc. Oct. 29, 1957 [Oct. 31, 1956], No. 33728/57. Classes 36, 37 and 38 (1). [Also in Group XXII] A method of attaching a metal member to an uncoated or metal coated ceramic, glass or semiconductor body comprises pressing the member against the body or coating at a temperature above 100 C. but below the softening point of the member or coating and of the body, and, where the body is a semi-conductor, below the eutectic temperature of the metal and semiconductor, and below the temperature at which dislocations are produced in the semi-conductor under the processing pressure used. The pressure used is such as to produce a 10-30% deformation of the metal member. The point may be made in the press shown in Fig. 1. The semiconductor member comprising a raised island is mounted on electrically heated press bed 24 and a pointed or wedge-shaped projection 16 on an electrically heated press head 10 presses a metal wire 18 against it. Wires of gold, silver, the eutectic alloy of aluminium and silicon, aluminium, copper, gold-plated copper, silver-plated gold, or aluminium coated with tin, antimony, indium or gallium may be bonded in this way to silicon and germanium. For example a gold wire may be bonded to a cleaned wafer of germanium using a deformation of 20% at a temperature of 200 C. sustained for a minute, if the entire treatment is carried out in hydrogen. In air, to obtain joints of comparable reliability, the heat and pressure should be maintained for 10 minutes. Suitable treatments for joining gold and aluminium to germanium, gold to silicon, and silver to barium titanate are also described. The transistor shown in Fig. 2 is formed as follows : A circular island is formed on a P-type Ge or Si body with a surface layer of N-type formed by impurity diffusion by masking the island and etching around it. Strips 44, 46 of aluminium and gold respectively are then alloyed to the island as shown and aluminium and gold wires 50, 48 pressure welded to the respective strips by the method described above to form emitter and base connections, a collector connection being made to the P-type base body. The electrodes are about 1 mil. apart. In a modification of this method the aluminium and gold wires are pressure welded direct to the surface of the island with a spacing of only 0.4 mils. In a further embodiment a gold or aluminium wire, the end of which has been softened and rounded by melting is pressure welded at its end to an N-type surface layer on a P-type body. The layer around the contact may then be etched away and a further contact pressure welded to the P-type material. The assembly may be heated momentarily after the pressure welding to the eutectic temperature of the wire and semi-conductor to produce an alloy junction. Sealing a metal to a glass or ceramic body.-A clean ceramic or glass tube 88 (Fig. 4) is inserted into the end of a clean " Kovar " (Registered Trade Mark) tube 90 and the overlapping parts of the tubes are clamped together between the jaws of the press head and bed 80, 82. To ensure a uniform radial pressure a plurality of spaced pairs of jaws may be used and a " Kovar " plug 89 inserted into tube 88 to prevent it from being crushed. The assembly is then heated at 300 C. for two hours under a pressure giving 10-20% distortion of the tube 88 to bond the tubes together. A row of metal terminals may be bonded to a glass or ceramic base member to form a terminal strip or to a barium titanate member to form a plurality of memory cells using a similar technique. Leads may in the same manner be connected to a circuit printed on a glass or ceramic base. Suitable combinations of pressure, temperature and duration of treatment for bonding silver to glass, steatite and an alumina based ceramic are also given in the Specification. Specification 881,834 is referred to.